The present invention relates to a method, computer program product, and apparatus for performing rendering.
Conventionally, medical image information relating to organs created by medical imaging devices, such as x-ray devices, computer tomography (CT) devices, magnetic resonance imaging (MRI) devices, and the like, are used in performing medical procedures such as medical diagnostics and treatment. Medical image information is processed to obtain an image which can be displayed three-dimensionally, and the image is viewed three-dimensionally for the purpose of diagnosis or treatment. For example, there are three-dimensional display methods as described below for displaying images of tubular organs among organs such as blood vessels, trachea, and digestive tract.
One such method is the parallel projective method which externally renders a tubular organ with parallel rays, and projects the tubular organ onto a two-dimensional plane. As shown in FIG. 1, a parallel projection image P1 created by the parallel projective method is suited for viewing a tubular organ from the outside. However, the user cannot view the interior of the tubular organ in the parallel projection image P1. The perspective projective method, for example, can be used for viewing the interior of a tubular organ. In the perspective projective method, an image of the interior of a tubular organ, rendered by rays radially radiated from a viewpoint set within the tubular organ, is projected onto a two-dimensional plane. The perspective projective image P2 shown in FIG. 2, for example, can be created by the perspective projective method. The perspective projective image P2 can be used as a virtual endoscope so as to display an image of the interior side of tubular organs just as if viewed through an endoscope. A user can view the inside of the tubular organ using the perspective projective image P2. However, when a user does not closely examine the entirety of the interior circumference of the tubular organ, there is concern a polyp or the like may be overlooked. Furthermore, it is difficult to see the back side of folds present in tubular organs in the perspective projective image P2.
An article by Vilanova Bartroli et al., “Virtual Colon Unfolding,” appearing in the United States publication, IEEE Visualization (2001, p. 411-420), describes an exfoliated picture display in which a tubular organ is projected onto a cylindrical projection surface virtually disposed around a tubular organ by the cylindrical projection method or the curved cylindrical projection method. The projection image is sliced from the side of the cylindrical surface so as to be exfoliated on a two-dimensional surface. An exfoliated picture P3, such as that shown in FIG. 3, is created by the exfoliated picture display. In the exfoliated picture P3, polyps and the like can be readily discovered since the inner wall surface of the tubular organ can be viewed on a two-dimensional surface.
For example, a cross-section of human tissue may be displayed by several different types of display methods using volume rendering. In this case, a user may compare various cross-sectional images for diagnosis. For example, a perspective projective image P2 showing a section of a human body including a tubular organ may be created, and an exfoliated picture P3 of the tubular organ displayed in the perspective projective image P2 may be created. The user may perform a medical examination using the perspective projective image P2 and exfoliated picture P3 displayed side by side. However, it is difficult to understand which location of the exfoliated picture P3 the perspective projective image P2, which is a cross-section image, corresponds to. Thus, it is difficult to associate the perspective projective image P2 with the exfoliated picture P3. For example, it is difficult to comprehend where a position in the cross-section observed in the perspective projective image P3 is located on the exfoliated picture P3, and conversely, it is difficult to comprehend where a position observed on the exfoliated picture P3 is located in the perspective projective image P2.